1. Field of the Invention
The present invention relates to an apparatus and method for determining position information of a mobile station (i.e., a mobile terminal), and more particularly to an apparatus and method for determining position information of a mobile station by controlling a mobile communication system to detect a propagation delay error.
2. Description of the Related Art
Currently, there is a need to detect the position mobile terminals in order to provide personal safety and increase personal business use. The Federal Communication Committee (FCC) has provided a method for allowing a mobile terminal and a mobile service system to estimate their position information. A plurality of international telecommunication standardization organizations have also provided methods in their standards as requirements for a mobile terminal, such that it is expected that such a method will be applicable to domestic mobile terminals and mobile communication systems.
Two methods have been developed for determining position information of a mobile terminal, i.e., a method for adapting a general signal for use in a mobile communication network, and a method for adapting signals created from a Global Positioning System (GPS) satellite developed by the US Department of Defense. There are a variety of signals obtainable from a mobile communication network, for example, a Time Of Arrival (TOA) signal for measuring a difference between propagation transmission times, a Time Difference of Arrival (TDOA) signal for measuring a difference between propagation transmission times of two base stations, and an Angle of Arrival (AOA) signal for measuring an arrival angle of a propagation signal, etc. An apparatus for calculating position information of a mobile terminal receives the above signals at the same time and detects distance and angle information between the mobile terminal and the base station in such a way that it can approximately determine a position of the mobile terminal using a triangular survey. A mobile terminal having a GPS chipset recognizes its own position using the GPS chipset, informs the base station of the recognized position information in such a way that it can estimate or determine its own correct position.
However, the aforementioned conventional apparatus where the mobile terminal adapts a GPS satellite signal to estimate its own position has the following disadvantages. Namely, because a navigation message created by the GPS satellite signal contains a low transfer rate and information associated with several satellites, it contains a large amount of information. Therefore, a long initial starting time is needed to determine position information of a mobile terminal assuming the system is initialized. In addition, the aforementioned conventional apparatus has a reception signal having a low signal strength so that it cannot create a high-strength signal for determining position information of the mobile terminal, resulting in difficulty in determining position information of the mobile terminal. The conventional apparatus typically determines a position of a mobile terminal upon receiving a request from a user instead of successively tracking the position of the mobile terminal, such that it consumes a long initial synchronization time to determine the position of the mobile terminal and cannot quickly determine the position of the mobile terminal. The mobile terminal adapts a battery as a power supply to guarantee its own mobility. However, it should be noted that the battery may be fully discharged prior to checking position information of the mobile terminal.
Therefore, there has recently been proposed a method for adapting a GPS satellite over a predetermined network. This method receives orbital information of the GPS satellite over a wireless network such as a mobile communication network at a high transfer rate, such that it can quickly find a GPS satellite signal and can enhance a possibility of determining a correct position of a mobile terminal. However, in order to acquire the correct position information of the mobile terminal even in a specific area covered by an essentially insufficient number of satellites, for example, an urban area where large and high buildings and numerous houses are densely crowded, it is preferable for a GPS signal to be combined with a mobile communication network signal.
According to the above conventional method for determining position information of the mobile terminal using either only the mobile communication network signal or both the mobile communication network signal and the GPS signal, individual signals (e.g., TOA, TDOA, and AOA signals) obtainable from the mobile communication network have high delay errors caused by terrestrial propagation transmission due to propagation attributes such as reflection, diffraction, and refraction. Specifically, the propagation signal is reflected, diffracted, and refracted due to buildings or topographic objects located between a base station and a mobile terminal, resulting in a large delay error. Particularly, the method for detecting specific time information such as TOA and TDOA signals compares a signal transmission time with a signal reception time to calculate the distance between the mobile terminal and the base station, resulting in an error proportional to a length of a propagation transmission path. Preferably, such time difference information can be acquired by a cross correlation between orthogonal Pseudorandom Noise (PN) codes. This method uses time difference information to calculate position information of a mobile terminal using a least-square method without considering a propagation delay error. Although the range of measuring the position of the mobile terminal is extended, the propagation delay error is unavoidably contained in an estimated position value of the mobile terminal in determining the position of the mobile terminal, resulting in a high position error due to deflection characteristics. In other words, it is difficult for the above conventional method to acquire desired accuracy of position information due to a difference in propagation environments.